Air springs generally comprise a piston and an endcap with an elastomer sleeve connected in an airtight manner between them. The sleeves may comprise cords embedded in the elastomer body. The cords are wound at a helix angle with respect to a sleeve centerline. The helix angle for each flexible member cord is substantially equal. Equal helix angles contribute to torsional strain and premature failure in air spring sleeves.
Composite sleeves are also known. They comprise a sleeve having a first flexible member connected in a partially overlapping manner to a second flexible member. Each flexible member having a different cord helix angle. The inner flexible member having a cord helix angle less that an outer flexible member cord helix angle with respect to a sleeve centerline.
Representative of the art is U.S. Pat. No. 5,975,506 (1999) to Thurow et al. which discloses an air spring having a composite flexible member in which cords are embedded as a reinforcement. The cord angle (a) in the first flexible-member is different from the cord angle β in the second flexible-member component. Cord angle (a) is less than cord angle β.
What is needed is an air spring sleeve having little or no torsional strain. What is needed is an air spring sleeve having a cord helix angle differential wherein the inner cord helix angle is greater than an outer cord helix angle. The present invention meets these needs.